Shelf



FIG. 1 is a perspective view showing the new design for a shelf;

FIG. 2 is a front view thereof;

FIG. 3 is a back view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof; and,

FIG. 6 is a side view thereof, the opposite side view being a mirror image of the side view shown. 

The ornamental design for a shelf, as shown and described. 